The present invention relates to improvements in plastic bags and fasteners therefor, particularly to a reclosable plastic film bag with a hermetically sealing tear strip at the top which is removable for use of the bag.
In the manufacture of plastic film bags, reclosable rib and groove profile elements have been provided which permit a bag to be opened and reclosed. Where the bags are used for containing products such as foodstuffs, flaps above the rib and groove elements have been joined to hermetically seal the bag until such time when it is purchased and opened for use. To facilitate opening, parallel lines of tear perforations have been placed above the rib and groove profiles so that a strip can be torn from the top to free the flaps and permit opening the bag by pulling the rib and groove elements apart. The addition of perforations to allow tearing a strip off the top has been known in U.S. Pat. Nos. such as 3,172,443, 3,226,787, 3,473,589 and 4,589,145.
Such perforations destroy the hermetic seal of the bag and permit the passage of air. While the rib and groove elements below the perforations may be joined to close and seal the bag, these elements may inadvertently become separated during handling, storage and merchandising so that air can enter the bag via the perforation holes. Further, the rib and groove elements per se may not be sufficiently airtight. The need for airtight integrity is especially so where the contents of the bag must be protected against air, such as where a bag contains foodstuffs, and laminated films are required. The addition of such perforations creates a problem because the rib and groove elements below said perforations may not, as indicated, be sufficiently airtight, though they present the best method of tearing off the top of the bag for access to the rib and groove elements. Other means of providing tear strips have been attempted, but these are not as satisfactory as the relatively simple expedient of perforating the film of the flaps at the bag top. Such perforations can be added by perforation equipment which operates rapidly and satisfactorily.
It is accordingly an object of the present invention to provide a bag structure and method of making the structure where the bag has reclosable rib and groove elements at the top, the flaps are joined to each other so as to provide a hermetic seal, perforations are included to be able to readily tear a strip off the top and yet the perforations do not admit air so as to jeopardize the hermetic seal of the bag.
A further object of the invention is to provide an improved bag structure which provides a reopenable bag which is positively sealed up to the time that the customer or user purchases the bag and tears a strip off the top.
A further object of the invention is to provide an improved simplified bag structure which can be inexpensively made and which provides for a sealed bag which has a reopenable feature.